One of the most serious problems today is that the natural disasters caused by the warming climate become increasingly severe, of which the major cause is that, the greenhouse gases increase day by day for using fossil fuels. Now, all the governments and enterprises in the world pay great attention to develop techniques about new clean energy source. At the same time, the Kyoto Protocol about energy utilization and limiting the emission of greenhouse gases is approved by more and more countries. How to increase the energy utilization efficiency and reduce the environmental pollution has become a problem that the countries in the world pay great attention to.
The fuel cell technology is currently one of the acknowledged core technologies in the energy technology field of the 21st century. The working principle of a fuel cell is to directly isothermally transform the chemical energy stored in fuels and oxidants into electrical energy. Comparing with a normal fuel engine, the fuel cell has the advantages of high efficiency, low noise, high reliability, and especially very low emission, which is considered as the currently preferred power generation technology that is clean and highly efficient. The fuel cell can be widely used in power plants, the automobile industry, or portable devices. For more detailed presentations about fuel cells, please refer to Int. J. Hydrogen Energy (22, No. 6, 601-610 (1997)) compiled by Hynek, et al., the thesis of J. A. Kerres, et al. in Journal of Membrane Science (185, 2001, 3-27), and the survey article of G. March in Materials Today (4, No. 2 (2001), 20-24).
Porous materials have a comparatively large specific surface area, and can adsorb more gas or small organic molecules that can be used as fuels. So, the development of porous materials is the most important thing in the field of key materials research of a fuel cell. Porous materials comprise microporous materials having pore size less than 2 nm, mesoporous materials having pore size between 2 nm and 50 nm, and macroporous materials having pore size bigger than 50 nm. In 1995, Omar Yaghi synthesized the MOF (metal-organic-framework) (referring to Nature, 1995, (378), 703), a metal-organic coordination polymer that is really close to practical application. As a new functional molecular material, the MOF not only has a crystal structure similar to the zeolite molecular sieve, but also its structure is capable of being designed. The MOF can obtain nano-size pore channels and cavities by directionally designing the topological structure and expanding the organic functional groups. So, it has great potential in applications of storing gas or organic molecules. However, the MOF has a comparative poor chemical stability. In 2005, Omar Yaghi disclosed the COF (covalent organic framework) (referring to Science, 2005, (310), 1166), an organic porous framework material, which is composed of light elements (C, H, O, B) being connected via covalent bonds. However, the chemical stability problem is not really solved.
Therefore, the performance of porous polymers is still to be improved further.